The present invention relates to a construction for the serial arrangement of individual fuel cells for implementing large-scale systems for generating electric power, and more particularly, to fuel cells in a flat configuration and combined into a number of blocks connected to form modular units and operatively associated with fuel gas and oxidation gas conducting devices, electric connections corresponding carrier structures, sealing elements and thermal insulation.
Fuel cells are power converters which generate electric energy (direct current at low voltage) from the chemical energy of reactants (fuel gas and oxidants) in a direct manner; that is, without a diversion via a thermodynamic cyclic process. In contrast to accumulators, in the case of fuel cells, the reactants are not integral constituents of the system which are gradually exhausted during the operation, but are continuously supplied, with the fuel cell having only a converter function.
Since the electrochemical processes on fuel cells take place on the surface and not within the volume, many individual cells must be integrated into a larger block for the purpose of achieving sufficient power output. Increasing world-wide efforts are therefore being made to develop the fuel cells in a space-saving flat construction which clearly permit more favorable investment costs because of the higher power density and because of manufacturing advantages. These blocks can easily be combined to form larger systems with a higher output.
The operating temperatures of the fuel cell depend on the materials used for the cells and range between 50.degree. C. (low temperature) and 1,000/.degree. C. (high temperature). In comparison to the low-temperature cells, the high-temperature cell has a number of advantages. In addition to a higher power generating efficiency, the high-temperature cells may also be used, for example, for the reversal process of high-temperature electrolysis. In this case, hydrogen can be obtained from water vapor at approximately 800.degree. to 1,000.degree. C. with a high efficiency. For this reason, the above-mentioned object is preferably based on high-temperature cells. However, the construction must also be suitable for low-temperature cells.
U.S. Pat. No. 4,476,196 describes an arrangement in which a parallelepiped-shaped fuel cell block with four gas connection elements (manifolds), which are fixed to the block by a ceramic paste, is disposed in a housing. An elastic insulation mechanically decouples and thermally insulates the block from the housing. A disadvantage of this solution resides in the four manifolds (two manifolds respectively for the fuel gas and two respectively for the oxidation gas) which require high expenditures with respect to gas conducting structures and which also increase the risk of failure. This solution may be acceptable for a laboratory operation or the operation of only a few units, but it is not suitable for a serial arrangement of many units and of an increased output because of the high expenditures and space requirements.
It is, therefore, an object of the present invention to develop a construction which permits a high packing density of the blocks and reduces the expenditures with respect to gas conducting structures. It is a further object of the present invention to ensure that, at any time, the blocks can be exchanged, and the individual elements can be serviced and monitored while keeping the costs low and the reliability high.
According to the present invention, the foregoing objects have been achieved in that the fuel cell blocks are provided with gastight connection elements for fuel gas and exhaust gas, and with metal pipes for feeding fuel gas and returning exhaust gas takes, and the fuel cell blocks being configured so as to require no connection elements for the conducting of the incoming and outgoing air because, as a result of the physical separation of the front side and the rear side of the fuel cells and the pressure difference between the front and rear sides, the air flows through the corresponding ducts of the individual fuel cells, and a carrier plate separates the spaces between the front side and the rear side and fixes the fuel cell blocks and the associated fuel gas conducting pipes.
An advantage of the present invention is the fact that only the fuel gas is fed to the block by special conduits and connection elements. In contrast, the oxidation gas (such as air) does not require this feeding of gas because the gas flow is generated from the outside pressure difference between the front side and the rear side of the fuel cell block.
With respect to the approach taken in the aforementioned U.S. patent, it is particularly advantageous in accordance with the present invention that a series of fuel cell blocks can be mounted on a carrier plate with integrated fuel gas ducts so that a completely tested and operable integrated module in a tank configured to allow air flow through the fuel cell elements without any additional gas conducting structures and due only to the pressure difference between the front side and the rear side.
A large number of blocks (for example, twelve) can be mounted on a flat carrier plate, in which case the fuel gas ducts are as extensively as possible an integral component of the carrier plate in order to reinforce it corresponding to system requirements. A direct feeding of the fuel gas into the blocks takes place by pipe pieces which are additionally mounted from the outside. In contrast, the air requires no separate pipe because the blocks are closed off tightly with the carrier plate. Due to the pressure difference between the front side and the rear side of the blocks, the gas flows automatically through the corresponding ducts of the fuel cells. For generating the pressure difference, the carrier plate is pushed into a gastight tank which contains corresponding chambers for the feeding and removal of the gas and prevents a flow under the carrier plate by way of sealing strips.